The subject matter of the invention finds applications in all those cases where a level measurement must be made from a distance, whether due to toxicity, hazard, high temperature or any other reason.
One typical but not restrictive application is reading the level of molten metal in an ingot mold in continuous casting processes.
In the present example, and when on top of the bath a protective powder is added, the normal known systems react negatively and above all do not ensure the required level reading and measuring accuracy and rapidity.
The present invention indeed attempts to realize a level measurement device having a high quality basic operation which can be further improved by means of suitable modifications and/or additions within the grasp of a person skilled in the art once the basic inventive concept is acquired.
According to the invention, the level measuring device utilizes a light source which projects a light beam on the medium whose level is to be measured.
The light spot is detected by a plurality of sensors (or, according to an alternative embodiment, by a particular sensor of a continuously linear or superficial form) along a line forming an angle with respect to the incident line of the light source.
With reference to a specific application, in itself very complex, which is given by way of example only, the invention will be hereinafter described in its particular construction details.
The specific exemplifying application is an ingot mold in a continuous casting plant.
According to the invention, the light source intensely illuminates a limited area of the surface.
The illumination system is opportunely devised in such a manner that the position of the light spot does not change relative to the surface whose level is to be measured even though the level itself may change.
The light spot is observed continuously and/or periodically by a receiver along a line positioned at an angle with respect to the axis of the mold or with respect to the light source's optical axis of incidence.
The geometrical configuration so realized permits the sensor to detect the variations in the vertical direction of the light spot when the level changes.
It is possible to ensure, by the use of auxiliary means, that the light sensitive element is not influenced by the surrounding light nor by the strong infrared emitted either by the refractory discharge conduit or by the covering powder in the phase of metering and restart.
The circuits used in the level measuring device, according to the invention, are devised in such a way as to execute a continuous or intermittent translation of the level to be measured into an electrical signal.
At the outlet of the measuring device, for instance, a variable voltage can be generated within predetermined limits, such variability being a function of the level, in the specific example, of the molten metal height contained within the control range.
According to the invention, there could also be provided alarm circuits and control circuits as well as other varied mechanisms.
Further according to the invention, the level measuring device is substantially composed by two sections, one section being the generator of continuous or intermittent light source as well as synchronization signals, and the other section being connected to the first section and including an angular position detector which converts the molten metal level into a voltage signal or other signal compatible with the apparatus downstream thereof.
According to a first preferential embodiment the light source generator section may include a variable frequency generator followed by a pulse generating circuit, such pulses being sent to means suitable for emitting the required illumination.
A light detector is connected in the neighbourhood of such illumination means, detects the efficiency of said means and emits a signal which is used as a clock for the processing of the signals.
The absence of said signal can actuate a device which effects the automatic substitution for the illumination means of a similar stand-by illumination means.
The position detector section can be replaced by a plurality of electro-optical or target sensors on which the image of the spot on the surface layer of the steel is projected.
The image of the light spot formed on said surface falls on, according to the height of the metal in the mold, a number of sensors, collimated with the projection angle formed by the path of the rays.
Each sensor is associated with circuits that select the rapidity of response suitable and necessary for the purpose of the invention.
According to the invention, a control system can be provided which controls the sensitivity of the photoelectric sensors (phototransistors).
Such a control system can be advantageously realized by illuminating said sensors by a continuous flood of light of a controlled intensity.
Such a polarized light can be produced by incandescent lamps whose intensity can be controlled with respect to the surrounding diffused light which covers the target in such a way as to maintain the basic polarization light of the photosensors constant.
According to the invention the photosensors output signals which are passed into a special filter and then converted into special signals which can be transmitted by relatively long electric lines to the rest of the circuits.
Such signals can be sent to a number of gates qualified enabled by the synchronizing strobe coming from the flash lamp in such a way as to read the logical level of the signals only in coincidence with the flashes produced by the lamp, thus eliminating unwanted disturbances.
According to the invention, there may also be provided circuits suitable for eliminating interference by impulsive disturbances whose fronts start occasionally in the strobing intervals.
Such circuits can provide a repetitive checking of the signal, since it is highly unlikely that a random disturbance starts two or more successive times during the strobing and is picked up by the same sensor.
According to the invention, after the verification circuits, there can be provided circuits which supply the voltage levels established in the outlet of the channels relative to the sensors and in relation to the intensity of the signal received by the sensors themselves.
These levels actuate a number of corresponding micro-switches, advantageously of solid state design, which supply a variable voltage which is a function of the position of the light spot on the illuminated photoelement.
When a plurality of adjacent sensors are illuminated simultaneously the output circuit can supply a signal proportional to the average voltage level related thereto, supplying thus, at the outlet either the value corresponding to the central photoelement of the group or the average value processed by the system according to the parameters introduced therein.
In the prior art as described by the EPO report No RS 60908 IT dated June 28, 1979, several patents are known which will be described hereinafter.
The U.S. Pat. No. 3,741,656 for Shapiro, describes a level measuring system for measuring the height of a substance in a container which does not provide movable parts nor elements in contact with said substance itself.
A variation in the substance height causes a variation in the detection angle between the light spot projected on the surface of the substance by a light source and an objective lens, which results in a displacement of the image of the light spot in relation to the centre of the lens itself, and a detector measures such displacement.
There are envisaged some light sources which send a light beam perpendicular or inclined with respect to the surface whose level is to be measured and detection systems which make use of the reflected light or that diffused by the surface itself.
The subject matter of the present patent application adopts a measuring system similar to that proposed by Shapiro, but for the detection purposes it uses only the light diffused by the surface.
The original idea is thus improved in order to render the detection independent of the intensity fluctuations of the diffused light and dependent only on the positions of the image of the light spot in relation to the centre of the lens the detection being independent of foreign light sources.
In fact the invention of Shapiro is inadequate and unsuitable for operating in ambients whereby there are disturbing external light sources.
The U.S. Pat. No. 3,867,628 for Brown describes a type of detector suitable only for measuring the variations in intensity of a pulsating frequency light source having a determined duration with a maximum and constant sensitivity in most ambient light conditions.
The detection sensor is kept at an optimal constant level of sensitivity by means of polarization obtained by a current generator regulated by the average level of light incident on the sensor itself.
A double-filtering system eliminates, from the pulsating outlet signal, all frequencies below and above a certain band.
This way the continuous component due to the ambient light is eliminated.
Nonetheless this does not eliminate light pulses emitted by light sources different from those predetermined sources and whose typical frequency is within the above said band (for example neon light, etc.), which may lead to an error in evaluating the intensity of the predetermined light source.
Such a system is uniquely utilizable in measuring the level of a substance in a container whereby the variation of the intensity of the pulsating radiation detected depends exclusively on the level variation.
Measurement systems which use the reflection or the diffusion of the light projected on the surface whose level is to be measured by a light source are useable in conjunction with the above indicated invention only in the case of constantly uniform surfaces and with a constant diffusing coefficient or deflection coefficient and in cases where the surroundings are void of fumes and dust of variable intensity and void of disturbances due to pulsating light.
The invention under consideration, by not basing the level measurement on the intensity variation of the detected light but only on the position of the image of the light spot produced by a pulsating source on the surface to be measured, is suitable for application even in dusty and smoky ambients with surfaces having variable levels with respect to time and space.
Besides, with the help of a feedback system it provides for eliminating all pulses which are not simultaneous with those generated by the light source, and if that proves to be insufficient, a memory and a selection circuit are able to distinguish as legitimate only those signals which are equally repeated during a certain number of successive flashes of the source since it is unlikely that an external signal frequency will coincide with that of the source. Accordingly the subject-matter of the invention is useable even in conditions where there are pulsating external sources of light.
The U.D.C. No. 666.1.031.228-55 for Kompan et al. describes an apparatus for measuring the level of a substance in a container which is based on the measurement of the intensity of light reflected by the surface whose level is to be measured.
A shutter with a rotating window positioned in front of a source of a continuous light generates two pulses of the same frequency but 180.degree. out of phase.
Each of these reflections from the surface strikes half a photo-electric element. In this case no output signal is generated.
When the level changes, the parts of the sensor are no longer equally illuminated and the device generates a suitable signal at the outlet.
Such invention operates on a level measuring principle completely different from that of the present invention, based on reflection and measuring the intensity of the reflected ray.
It can not offer a guarantee of indifference to the optical and mechanical disturbances as offered by the present invention.
The use of moving parts renders that invention even less reliable.
The U.S. Pat. No. 3,838,727 for Levi Shuckarczuk proposes a system of measurement of a molten metal level in a container based on the variation in the intensity of the radiation which strikes a detector when the level itself varies.
The detected radiation is emitted by the substance itself, and the detector "sees" simultaneously, through a window, both a portion of the metal surface and a lateral part of the container. When the level changes the proportions between the metal surface and the container as seen by the detector vary and hence a variation in the intensity of the radiation detected takes place.
This invention does not use a suitable light source and is thus useable only for molten metal baths which are not covered by dust and for smokeless conditions without external disturbances.
The present invention utilizes instead a suitable light source and is also useable in the case mentioned above.
The Pat. No. 745587 for Poncet describes a level measuring device for molten metal in a continuous casting mold, which device makes use of the radiation emitted by the molten metal surface and which is only partially sensitive to disturbances by the jet of metal being poured into the mold itself and the flame.
A lens, whose axis is arranged obliquely in relation to the axis of the mold, produces an optical image of the bath surface; of the pouring jet and part of the lateral surface of the mold.
From such an image, one or more sensors use the most extreme part of the pouring jet and, more specifically, are positioned between the image of the molten metal's surface contour when this is at an optimal level.
Variation in the metal level causes a variation in the illumination of the sensor and consequently a variation in its response.
The sensitivity to the radiation emitted by the pouring jet can be further diminished by increasing the number of sensors and arranging them in a suitable manner.
To avoid disturbances generated by the flames, detectors particularly sensitive to infrared rays are employed.
The subject matter of the present invention does not utilize; for the detection, the radiation emitted by the casting bath, but the radiation produced by a suitable source of pulsating light diffused on the surface of the molten metal.
Besides, for the measurement of the level, it does not exploit the variation of the detected radiation intensity, but only the variation in the position of the small light spot produced on the surface of the liquid by the pulsating light source, which spot is focused by a lens on a suitable sensor.
The device of the present application is therefore by no means sensitive to the radiation emitted by the pouring jet as well as the presence of any flame.
It is also utilizable in smoky surroundings as well as in conditions where there are anti-oxidizing dusts on top of the molten metal.
The present invention therefore consists of a level reader suitable for measuring the level of any substance, advantageously dangerous substances whether due to heat, toxicity or other reasons, and with or without anti-oxidizing superficial layers, characterized by presenting in reciprocal coordination and cooperation:
a source of intense light illuminating a restricted and localised area on the surface of the medium whose level is to be measured; PA1 a processing receiver arranged so that at least part of the optical control axis is at an angle in relation to said light source, there being advantageously included one or more regulation means responsive to the ambient light, regulation means responsive to infrared rays or the light, alarm means and control means.